April 7, 2011

760 Thunderstorms Recorded Per Hour

by ssavage

Scientists have calculated that the Earth sees about 760 thunderstorms every hour.

The figure is substantially lower than numbers that have been used for nearly a century.

The new research, which was unveiled at a recent European Geosciences Union meeting, uses a global network of monitoring stations that detect the electromagnetic pulses produced by major bolts of lightning.

The scientists confirmed that thunderstorms are mainly a tropical phenomenon, and the Congo basin is the global hotspot.

Thunderstorms also track the passage of sunlight across the world, with sunny conditions producing greater convection in the air.

"The monitoring stations might miss some bolts of lightning, but we think we're getting the big ones - and that's enough to tell you where the thunderstorms are," said Colin Price, head of the Geophysics and Planetary Sciences department at Tel Aviv University in Israel.

"And so with this global network we're able to improve on numbers that have been in standard use since the 1920s."

The first attempt to estimate thunderstorm numbers is thought to have been made by CEP Brooks in 1925.

During that time it was customary for weather stations to note days when thunderstorms occurred nearby.

He calculated there were around 1,800 per hour on average across the world.

However, his research suffered incomplete data and mistaken assumptions.

OH Gish and GR Wait flew over the top of 21 thunderstorms in the U.S. in the 1950s carrying equipment capable of measuring voltages and currents in the air.

They came up with a global figure of 2,000 to 3,600 per hour.

The new research uses a completely different technique, with over 40 stations around the world geared up to detect electromagnetic pulses produced by strong lightning bolts.

Triangulating from groups of stations enables the World Wide Lightning Location Network (wwlin.net) to help determine the location of the flashes.

A computer algorithm is deployed to assign flashes to their separate parent storms when they are clustered.

Analyzing this data for September 2010 produced the average hourly figure of 760.

Thunderstorms cluster in the center of continents in the tropics, with the Congo basin standing out.

"That's perhaps because it's drier there than in the Amazon, for example - thunderstorms seem to form more easily in drier conditions," Price told BBC News.

The network is looking to add new observation points to improve results, and recently initiated a program to detect explosive volcanic eruptions through the lightning flashes that occur in the ascending plumes of hot ash.